Soybean response to copper applied to two soils with different levels of organic matter and clay

Increasing the amount of soil organic matter (OM) alters the availability of copper (Cu) for plants under tropical and subtropical conditions. With the aim of evaluating the effects of the OM/Cu interaction on the soybean crop, a trial was conducted with a fully randomized 2 x 5 factorial design and four replicates. The treatments consisted of five Cu rates (0, 1, 2, 4 and 8 mg kg(-1)) and two soil types: Typic Oxisol and Typic Ultisol. The soybean responded to fertilization with Cu, producing the highest estimated grain yield at a rate of 4.1 mg kg(-1). Similarly were also observed for shoot dry weight, number of pods and root length. The soil chemical properties and nutrient levels in the leaves and grain were influenced only by the soil type, whereas physiological components were affected in terms of photosynthetic rate and intercellular CO2 concentration.